docs: Add CLAUDE.md for Claude Code guidance

Author: ericc-ch

CLAUDE.md

@@ -0,0 +1,37 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Development Commands
+
+- **Install dependencies**: `bun install`
+- **Build**: `bun run build`
+- **Dev server (watch)**: `bun run dev`
+- **Production start**: `bun run start`
+- **Lint**: `bun run lint`
+- **Pre-commit lint/fix**: Runs automatically via git hooks (bunx eslint --fix)
+
+## Architecture Overview
+
+- **Entry point**: `src/main.ts` defines CLI subcommands (`start` and `auth`) for the Copilot API server and authentication flow.
+- **Server**: `src/server.ts` sets up HTTP routes using Hono, maps OpenAI/Anthropic-compatible endpoints, and handles logging/cors.
+- **Routes**: Handlers for chat completions, embeddings, models, and messages are under `src/routes/`, providing API endpoints compatible with OpenAI and Anthropic APIs.
+- **Copilot communication**: `src/services/copilot/` contains methods for proxying requests (chat completions, model listing, embeddings) to the GitHub Copilot backend using user tokens.
+- **Lib utilities**: `src/lib/` contains configuration, token, model caching, and error handling helpers.
+- **Authentication**: `src/auth.ts` provides the CLI handler for authenticating with GitHub, managing required tokens, and persisting them locally.
+
+## API Endpoints
+
+- **OpenAI-compatible**:
+  - `POST /v1/chat/completions`
+  - `GET /v1/models`
+  - `POST /v1/embeddings`
+- **Anthropic-compatible**:
+  - `POST /v1/messages`
+  - `POST /v1/messages/count_tokens`
+
+## Other Notes
+
+- Ensure Bun (>= 1.2.x) is installed for all scripts and local dev.
+- Tokens and cache are handled automatically; manual authentication can be forced with the `auth` subcommand.
+- No .cursorrules, .github/copilot-instructions.md, or .cursor/rules found, so follow typical TypeScript/Bun/ESLint conventions as seen in this codebase.